Photo-sensing reflectors for compact display module assembly

ABSTRACT

Techniques are provided to reduce the form factor of laser-based systems by multi-purposing a photodiode used to help control the output of a laser. A reflective photodiode comprises a light receiving surface and a reflective coating. The light receiving surface is configured to absorb some incident light and to convert it into electrical current. The reflective coating is disposed on the light receiving surface and is configured to reflect some of the incident light away from the light receiving surface. The reflective coating also permits some of the incoming light to pass therethrough for absorption.

BACKGROUND

A laser is a type of device that generates a beam of coherent light.Most lasers include a resonant cavity that is defined by the structureof the laser and that spans the length of the laser. When current isinjected into the laser, spontaneously emitted photons are generated.Some of these spontaneously emitted photons will successfully couple tothe laser's resonant cavity. Provided that the laser is biased above itslasing current threshold, the photon density will increase inside of theresonant cavity and eventually a pulse of laser light will be generatedand emitted from the laser.

Lasers can be used in many different applications. For instance, laserscan be used for communication, biomedical imaging, precision metrology,and even for generating images, such as for virtual-reality oraugmented-reality (collectively “mixed-reality”) systems.

In many scenarios/applications, especially in mixed-reality systems, alaser operates in conjunction with one or more collimating optic(s),beam combiner(s) (e.g., a dichroic prism), and photodiodes. Forinstance, many mixed-reality systems use a red, green, blue (RGB) laserto generate virtual image content for the mixed-reality scene. The laserlight generated by the RGB (and/or IR) lasers is often collimatedthrough a collimating optic and then spectrally/optically combined via abeam combiner. To finely control the output of the laser (especially dueto changing operational conditions such as changes to the laser's lasingcurrent threshold or its slope efficiency), a portion of the laser'slaser light is also often measured by a photodiode.

As laser-based systems become more advanced, it is becoming more andmore desirable to employ lasers and associated components (e.g.,collimating optics, beam combiners, and photodiodes) that havesmall/smaller form factors. Use of smaller units means that morehardware can be packaged together at reduced costs. Accordingly, thereis a substantial need in the field to reduce the size of laser-basedsystems and/or to improve the arrangement/positioning of the componentsrelative to one another.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one exemplary technology area where some embodimentsdescribed herein may be practiced.

BRIEF SUMMARY

Embodiments disclosed herein relate to systems, methods, and devicesthat can be used to reduce the form factor of laser-based systems byre-purposing, or rather multi-purposing, a photodiode that is used tohelp control the output of a laser.

In some embodiments, a reflective photodiode comprises a light receivingsurface and a reflective coating. The light receiving surface isconfigured or structured to absorb a first portion of incoming orincident light that is directed at the reflective photodiode and toconvert the first portion into electrical current. The reflectivecoating is disposed on the light receiving surface and is configured toreflect a second portion of the incoming light away from the lightreceiving surface, thereby operating as a turning optic. In addition toreflecting some of the light, the reflective coating is also configuredto permit some of the incoming light (e.g., the first portion) to passthrough the reflective coating to be absorbed by the light receivingsurface.

In some embodiments, an illumination system is provided, where theillumination system renders images for a mixed-reality system. Thisillumination system includes a laser assembly, a microelectromechanicalscanning (MEMS) mirror system, and a reflective photodiode. The laserassembly includes at least one red, green, and blue (RGB) laser and/oran infrared (IR) laser. The MEMS mirror system is configured to redirectlaser light generated by the laser assembly to illuminate pixels in animage frame for the mixed-reality system. The reflective photodiodeincludes the light receiving surface and the reflective coatingdescribed above. Furthermore, the reflective coating is configured toreflect incoming light away from the light receiving surface towards theMEMS mirror system.

In some embodiments, an illumination system is provided, where theillumination system renders images for a mixed-reality system byindividually scanning individual pixels for the rendered images. Thisillumination system includes a laser assembly, a MEMS mirror system, abeam combiner, one or more collimating optic(s), and a reflectivephotodiode. The laser assembly includes red, green, and blue (RGB)laser(s). The MEMS mirror system is configured to redirect laser lightgenerated by the laser assembly to illuminate pixels in an image framefor the mixed-reality system. The beam combiner is configured to combinethe laser light generated by the laser assembly. The collimating opticsare designed to collimate the laser light generated by the laserassembly. The reflective photodiode includes the light receiving surfaceand the reflective coating described earlier.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

Additional features and advantages will be set forth in the descriptionwhich follows, and in part will be obvious from the description, or maybe learned by the practice of the teachings herein. Features andadvantages of the invention may be realized and obtained by means of theinstruments and combinations particularly pointed out in the appendedclaims. Features of the present invention will become more fullyapparent from the following description and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features can be obtained, a more particular descriptionof the subject matter briefly described above will be rendered byreference to specific embodiments which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments and are not therefore to be considered to be limiting inscope, embodiments will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1A illustrates a system that uses a beam combiner (e.g., a dichroicprism/mirror) to combine laser light, where a portion of the laser lightis permitted to pass or leak through the beam combiner and be directedto one or more photodiode(s) that then measure an output of the laseremitters that emitted the laser light.

FIG. 1B illustrates how different light sources can be used with theMEMS mirror system, where the light sources can be red, green, blue, orinfrared laser emitters/assemblies.

FIG. 2A illustrates an improved illumination system that re-purposes, orrather multi-purposes, a photodiode by configuring the photodiode tooperate as a reflective photodiode that both (i) operates as aphotodiode by absorbing laser light to determine an output of a laseremitter and (ii) operates as a turning optic by reflecting light. FIG.2A also shows how the reflective photodiode may be positioned within theillumination system between a light source and a beam combiner andbetween the light source and a collimating optic.

FIG. 2B illustrates how the reflective photodiode may be positionedwithin the illumination system between a collimating optic and a beamcombiner.

FIG. 2C illustrates a compact RGB module with a turning optic. Here, thephotodiode/turning optic combination can individually sample the red,green, and blue laser colors, or, alternatively, a singlephotodiode/turning optic combination may be provided to sample all lasercolors.

FIG. 2D illustrates another example arrangement/placement of thereflective photodiode, where the reflective photodiode is positioneddownstream of both the collimating optic(s) and the beam combiner(s).

FIG. 2E illustrates a scenario in which a single collimating optic isprovided to concurrently collimate the laser light from multipledifferent light sources.

FIG. 3A illustrates how the reflective photodiode includes a highlyreflective (HR) coating and a light receiving surface, where the HRcoating is configured to reflect light while the light receiving surfaceis configured to absorb and measure light.

FIG. 3B illustrates a sample measurement of the reflectivity propertiesfor the reflective coating of a reflective photodiode.

FIG. 4 illustrates a multi-section reflective photodiode that includesmultiple photodiode sections, where each section is able tosimultaneously receive a corresponding incident beam of light.

FIG. 5A illustrates a flowchart of an example method for providingfeedback to a laser (e.g., a light source) based on light measurementsdetermined by a reflective photodiode, where the light measurements areable to accurately determine operational characteristics of the laser(e.g., the lasing current threshold and slope efficiency) and thefeedback is provided to more accurately control operations of the laserbased on the operational characteristics.

FIG. 5B illustrates how the optical flatness of the reflectivephotodiodes is very flat and how the surface roughness of the reflectivephotodiodes is very low. Having flat optical flatness and low surfaceroughness allows the reflective photodiode to exhibit highly beneficialreflective properties, thus allowing it to operate as a turning optic.

FIG. 6 illustrates an example technique in which the reflectivephotodiode is providing feedback to the light source, where the feedbackincludes information detailing or describing the operationalcharacteristics (e.g., power output, lasing current threshold, slopeefficiency, etc.) of the light source, as measured by the reflectivephotodiode.

FIG. 7A illustrates how a microelectromechanical scanning (MEMS) mirrorsystem may be used in conjunction with a laser and its associated beamforming and measuring components (e.g., collimating optics, beamcombiners, photodiodes, etc.) in order to produce virtual images for amixed-reality system.

FIG. 7B provides additional detail regarding the operations of a MEMSmirror system within a mixed-reality system.

FIG. 8A illustrates an example of a MEMS/laser system being used in a VRsystem having a display, and FIG. 8B illustrates an example of aMEMS/laser system being used in an AR system having a waveguide display.

FIG. 9 illustrates an example computer system that is operable tocontrol the components described herein.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to systems, methods, and devicesthat can be used to reduce the form factor of laser-based systems bymulti-purposing a photodiode used to help control the output power of alaser.

In some embodiments, a reflective photodiode comprises a light receivingsurface and a reflective coating. The light receiving surface absorbssome incident light and converts it into electrical current. Thereflective coating is disposed on the light receiving surface andreflects some of the incident light away from the light receivingsurface. The reflective coating also permits some of the incoming lightto pass therethrough for absorption.

In some embodiments, an illumination system includes a laser assembly, aMEMS mirror system, and a reflective photodiode. The laser assemblyincludes RGB laser(s) and/or IR laser(s). The MEMS mirror systemredirects laser light generated by the laser assembly to illuminatepixels in an image frame. The reflective photodiode includes the lightreceiving surface and the reflective coating described above, where thereflective coating reflects some of the incoming light towards the MEMSmirror system.

In some embodiments, an illumination system includes a laser assembly, aMEMS mirror system, a beam combiner, collimating optic(s), and areflective photodiode. The laser assembly includes RGB laser(s) whichemit laser light. The MEMS mirror system redirects this laser light toilluminate pixels in an image frame. The beam combiner combines thelaser light, and the collimating optic(s) collimate the laser light. Thereflective photodiode includes the light receiving surface and thereflective coating described earlier.

Technical Benefit(s)

The disclosed embodiments bring about substantial benefits to thetechnical field. In particular, the disclosed embodiments multi-purposea photodiode by coating it with a highly reflective (HR) coating. Thisreflective coating allows some light to pass through it so the light canbe absorbed by the photodiode, which can then determine the laserassembly's power output and other operational characteristics (e.g.,lasing current threshold, slope efficiency, etc.). Additionally, thereflective coating is configured to reflect other portions of the light.By so doing, the photodiode is now a “reflective photodiode” capable ofconcurrently operating as both a photodiode and a turning optic (i.e. adevice that reflects light out of plane relative to the direction ofincident/incoming light). In this regard, the disclosed embodimentsaggregate or combine multiple discrete units into a single unit, therebyreducing the amount of hardware provided within a laser-based system.Whereas previous systems relied on separate turning optics and separatephotodiodes, the disclosed embodiments are able to beneficially combinethese components into a single unit, thereby saving space and reducingcosts.

The disclosed embodiments also improve the technical field by optimizingthe placement of this improved reflective photodiode within anillumination system. For instance, because the photodiode now has dualor multiple purposes, it can now be placed at locations where itpreviously could not be placed. Enabling this reflective photodiode tobe placed at multiple different locations allows for more flexibility inhow the illumination system is designed. Increased design flexibilityalso helps reduce cost, reduce time spent in designing the system, andreduce constraints that were previously imposed on the illuminationsystem. In this regard, the disclosed embodiments provide substantial,real-world practical applications and benefits to the technical field.

Additional benefits include the photodiode being able to be positionedwithin the system in order to provide feedback control for the laserdevice. That is, because laser performance changes over temperature andtime, it is highly beneficial to continuously or periodicallymeasure/determine the laser's performance by monitoring its power outputand other parameters via the use of the photodiode. In doing so, theembodiments are able to accurately determine the laser's lasing currentthreshold (i.e. the point at which the laser will begin to lase) as wellas its slope efficiency (i.e. the relationship between the laser'spump/drive current and its power output). As such, using the disclosedphotodiode will result in a more accurate, robust, and reliablelaser-based system. It will also enable independent monitoring andcontrol of a laser assembly/emitter without significantly increasing thesize of the laser-based system's package. As used herein, the terms“laser,” “laser assembly,” and “laser emitter” are interchangeable withone another.

Leaking Light Through A Beam Combiner

FIG. 1A illustrates an illumination system 100 in which light is leakedthrough a beam combiner (e.g., a dichroic prism/mirror) and absorbed bya photodiode, which is used to determine a laser's power output, asdescribed earlier.

To illustrate, illumination system 100 includes light source 105A, lightsource 105B, and light source 105C. Turning briefly to FIG. 1B, lightsource 145, which is representative of light sources 105A, 105B, and105C, may include different types of light sources. Examples include,but are not limited to, a red laser 150, a green laser 155, a blue laser160, an infrared (IR) laser 165, or any combination of the above.

Returning to FIG. 1A, light sources 105A, 105B, and 105C are configuredto emit light, such as light 110A, light 110B, and light 110C,respectively. Light 110A, 110B, and 110C then each pass through acorresponding collimation optic, as shown by collimation optic 115A,collimation optic 115B, and collimation optic 115C, thereby producingcollimated light 120A, 120B, and 120C.

Illumination system 100 then includes a beam combiner in the form ofdichroic prisms 125A, 125B, and 125C. Portions of collimated light 120A,120B, and 120C reflect off of dichroic prisms 125A, 125B, and 125C andare spectrally/optically combined by the dichroic prisms 125A, 125B, and125C to produce combined laser light 130.

Other portions of light (e.g., light portions 135A, 135B, and 135C) areleaked or passed through the dichroic prisms 125A, 125B, and 125C. Theselight portions 135A, 135B, and 135C are then absorbed by photodiodes140A, 140B, and 140C, respectively. By absorbing light portions 135A,135B, and 135C, the photodiodes 140A, 140B, and 140C are able todetermine the power output and operational parameters of the lightsources 105A, 105B, and 105C. In some embodiments, photodiodes 140A,140B, and 140C include an anti-reflective (AR) coating that isconfigured to absorb some or all of the light presented to them. Thisdetermination allows the illumination system 100 to dynamically adjustor modify the output of the light sources 105A, 105B, and 105C toproduce improved image quality or improved laser performance, especiallyin response to changes to lasing current threshold or slope efficiency.

The disclosed embodiments presented herein improve the architecturepresented in FIG. 1A by multi-purposing a photodiode to operate as botha photodiode and a turning optic. As used herein, a “turning optic”refers to an optical device that is able to receive incident light andreflect or aim it at a different location. As will be described in moredetail later, the reflected light may be reflected at any angle (e.g.,acute and obtuse angles).

This improved photodiode is referred to herein as a “reflectivephotodiode.” Use of this reflective photodiode allows an illuminationsystem to position the photodiode at locations where it previously couldnot be placed. Furthermore, use of this reflective photodiode allows fora more compact laser-based system (e.g., because light can be reflectedout of plane, the components can be packaged closer to one another),resulting in the benefits described earlier.

“Reflective Photodiode” Characteristics

FIG. 2A illustrates an improved type of illumination system 200A.Illumination system 200A includes a light source 205, which isrepresentative of the light sources 105A, 105B, and 105C from FIG. 1Aand light source 145 from FIG. 1B. Here, light source 205 is shown asemitting laser light 210.

As used herein, the term “laser light” should be interpreted broadly,unless specifically specified otherwise. For instance, laser light caninclude a single laser color (e.g., any one of a red, green, blue, or IRlaser light). Laser light can also include multiple colors (e.g., anycombination of red, green, blue, or IR light). Laser light can begenerated by a single light source (e.g., a single laser emitter) or, incases where the laser light is a combination of multiple colors, thelaser light may be generated by multiple different light sources. Insome cases, the laser light includes a single color, but multiple lightsources were used to generate the laser light. Accordingly, as usedherein, “laser light” should be interpreted broadly to cover any ofmultiple different types of laser light.

As shown, laser light 210 is being directed towards a reflectivephotodiode/turning optic 215. Reflective photodiode/turning optic 215 isshown as including a reflective coating 220 and a light receivingsurface 225.

Here, the light receiving surface 225 is configured to absorb a firstportion (e.g., light portion 230) of incoming light (e.g., laser light210) that is directed at the reflective photodiode/turning optic 215 andto convert the first portion (e.g., light portion 230) of incoming lightinto electrical current. To clarify, a photodiode is a type ofsemiconductor device that converts light into an electrical current.This electrical current is generated by the semiconductor device whenlight (or rather photons) is absorbed on the photodiode's lightreceiving surface (e.g., light receiving surface 225). A photodiodeincludes a p-n junction. When a photon strikes or hits the photodiode,then an electron-hole pair is formed within the p-n junction, creating aphotoelectric effect. Holes move towards the p-n junction's anode whilethe electrons move toward the p-n junction's cathode, thereby creating aphotocurrent. Accordingly, reflective photodiode/turning optic 215 isable to convert light into electrical current. As will be described inmore detail later, this electrical current is used to measure theoperational characteristics (e.g., lasing current threshold, slopeefficiency, power output, etc.) of the light source 205. Furthermore,the measurements and analysis of the electrical current can be providedas feedback to the light source 205 in order to more accurately controlthe operations of light source 205.

Reflective coating 220, which is coated over-top-of or disposedover-top-of (or on) the light receiving surface 225, may be any type ofreflective coating capable of reflecting light while also allowing atleast some of the light to pass through it. It will be appreciated,therefore, that reflective coating 220 (i.e. a type of high reflectivecoating) is distinctive from the anti-reflective coating that may bepresent on photodiodes 140A, 140B, and 140C from FIG. 1A. For instance,FIG. 2A shows how light portion 230 leaks or otherwise passes throughreflective coating 220. FIG. 2A also shows how reflected light 235 isreflected off of the reflective coating 220. As such, reflective coating220 is able to simultaneously reflect light and allow light to passthrough it. Accordingly, reflective coating 220 is configured to reflecta second portion (e.g., reflected light 235) of the incoming light(e.g., laser light 210) away from the light receiving surface 225 whilepermitting the first portion (e.g., light portion 230) of the incominglight to pass through the reflective coating 220 and to be absorbed bythe light receiving surface 225.

In some cases, reflective coating 220 is configured to reflect at least80% of the incoming/incident light (i.e. reflected light 235 constitutes80% of the laser light 210, which has been reflected). In some cases,reflective coating 220 is configured to reflect at least 90% of theincoming/incident light. In some cases, reflective coating 220 isconfigured to reflect at least 95%, 96%, 97%, 98%, or even 99% of theincoming/incident light. In this regard, the second portion (i.e.reflected light 235) of the incoming light (i.e. laser light 210)constitutes a majority of the incoming/incident light such that themajority of the incoming light is reflected by the reflective coating220 while the first portion (i.e. light portion 230), which passesthrough the reflective coating 220 and which is absorbed by the lightreceiving surface 225, constitutes a minority of the incoming light.Accordingly, reflective photodiode/turning optic 215 reflects a majorityof the laser light generated by light source 205 while permitting aminority of the laser light to be absorbed by its light receivingsurface 225. Relatedly, in some instances, the first portion (e.g.,light portion 230) of the incoming light that is absorbed by the lightreceiving surface 225 is less than 20%, 10%, 5%, or even about 3% of theincoming light.

Reflective photodiode/turning optic 215 is labeled as being both aphotodiode and a turning optic as a result of it having multiplefunctions or purposes (e.g., reflection and absorption). FIG. 2A alsoshows reflective photodiode/turning optic 215 reflecting laser light 210at about a 90-degree angle. It will be appreciated, however, that thelight may be reflected at any angle and is not limited to a 90-degreeangle. For instance, the light may be reflected at any acute angle(e.g., between 0 degrees and 90 degrees) or at any obtuse angle (e.g.,greater than 90 degrees). As such, the embodiments are able to reflectlight at any angle and are not limited to any particular angle orconfiguration. Accordingly, reflective photodiode/turning optic 215constitutes a type of turning optic that reflects at least a portion ofincoming light to a different direction.

FIG. 2A also shows that the illumination system 200A includes acollimating optic 240A and a beam combiner 245 (e.g., perhaps a dichroicprism/mirror). Reflected light 235 is shown as being reflected off ofreflective coating 220 and being directed or aimed at collimating optic240A.

A collimating optic (e.g., collimating optic 240A) is a type of opticaldevice that narrows a light beam. This narrowing effect is achieved byeither aligning light rays to follow a particular direction (e.g., tocause the rays to be parallel or somewhat parallel) and/or to cause thespatial cross section of the light beam to become relatively smaller.

After the reflected light 235 passes through the collimating optic 240A,then it is shown as striking beam combiner 245. Beam combiner 245 (e.g.,a dichroic prism/mirror) is another type of optical device. This opticaldevice is capable of combining the light rays from multiple differentlight beams in order to form a single light beam. As an example, beamcombiner 245 is able to combine the laser light from any combination ofa red laser, a green laser, and a blue laser to form combined RGB light.It can also combine RGB light with IR light. Therefore, while beamcombiner 245 is not shown in FIG. 2A as combining multiple beams oflight, it will be appreciated that beam combiner 245 is able to combinelight (e.g., as shown by dichroic prisms 125A, 125B, and 125C (i.e.types of beam combiners) in FIG. 1A).

Flexible Placement of the Reflective Photodiode Within an IlluminationSystem

As a result of having multiple functionalities or multiple purposes,reflective photodiode/turning optic 215 can now be placed at numerousdifferent locations within illumination system 200A. FIG. 2A shows oneexample placement.

Here, reflective photodiode/turning optic 215 is positioned upstream ofthe beam combiner 245 such that reflective photodiode/turning optic 215is positioned between the light source 205 (e.g., a type of laserassembly/emitter) and the beam combiner 245 relative to a path of lightemitted from the light source 205 towards the beam combiner 245. FIG. 2Aalso shows that the reflective photodiode/turning optic 215 ispositioned upstream of the collimating optic 240A such that thereflective photodiode/turning optic 215 is positioned between the lightsource 205 and the collimating optic 240A relative to a path of lightemitted from the light source 205 towards the collimating optic 240A.

As a result of being positioned upstream of the collimating optic 240A,the reflective photodiode/turning optic 215 is positioned at apre-collimation location within the illumination system 200A.Consequently, the laser light is collimated after being received at, orreflected by, the reflective photodiode/turning optic 215.

FIG. 2B shows another example placement location for the improvedreflective photodiode within an illumination system 200B. Specifically,FIG. 2B again shows the light source 205, a collimating optic 240B(which is representative of the collimating optic 240A from FIG. 2A butnow positioned at a new location), the reflective photodiode/turningoptic 215, and the beam combiner 245. Here, the reflectivephotodiode/turning optic 215 is positioned downstream of the collimatingoptic 240B and upstream of the beam combiner 245. That is, thereflective photodiode/turning optic 215 is positioned between thecollimating optic 240B and the beam combiner 245.

As a result of being positioned downstream of the collimating optic240B, the reflective photodiode/turning optic 215 is positioned at apost-collimation location within the illumination system 200B.Consequently, the laser light is collimated prior to being received at,or reflected by, the reflective photodiode/turning optic 215.

FIG. 2C provides an example illustration of another illumination system200C that includes a compact RGB module 250. Compact RGB module 250includes a reflective photodiode 255 and multiple different lightsources (e.g., light sources 260A, 260B, and 260C), which arerepresentative of the reflective photodiodes and light sources discussedearlier. With this compact arrangement or profile, the reflectivephotodiode 255 can individually sample red color laser light, greencolor laser light, and/or blue color laser light. Alternatively, thereflective photodiode 255 may jointly or concurrently sample all of thelaser light colors.

FIG. 2D illustrates yet another example configuration for anillumination system 200D. Illumination system 200D includes lightsources 265A, 265B, and 265C, a collimating optic 270 (more areillustrated but not labeled for brevity purposes), a beam combiner 275(again more are illustrated but not labeled), and a reflectivephotodiode 280. In this scenario, the reflective photodiode 280 ispositioned downstream of the collimating optic 270 and downstream of thebeam combiner 275. In this regard, illumination system 200D is somewhatsimilar to illumination system 100, but illumination system 200D nowincludes the improved reflective photodiode. FIG. 2D also shows how thereflective photodiode 280 is able to reflect light in the form ofreflected light 285. Reflected light 285 can be directed towards anyother downstream component or entity (e.g., a MEMS mirror system, to bediscussed later).

While some of the earlier figures illustrated scenarios in which eachred, green, and blue laser was associated with its own correspondingcollimating optic, that may not always be the case. For instance, FIG.2E shows a scenario in which a single collimating optic 290 is providedto jointly or concurrently collimate the laser light from multipledifferent light sources. As such, some embodiments are structured toinclude multiple collimating optics (e.g., one for each light source)while other embodiments are structured to include a single collimatingoptic that collimates light for multiple light sources.

Accordingly, as a result of multi-purposing a photodiode to operate asboth a photodiode and a turning optic, the improved reflectivephotodiode can be beneficially/flexibly placed at multiple locationswithin an illumination system. This increased flexibility provides amore robust and dynamic system capable of adapting to many differentscenarios.

Light Properties And Attributes of the Reflective Photodiode

Attention will now be directed to FIG. 3A, which initially shows a lightsource 300 that is representative of any of the earlier light sourcesdiscussed thus far. Here, light source 300 is shown as projecting a beamor ray of light in the form of incident light 305. Incident light 305 isbeing directed towards reflective photodiode 310, which isrepresentative of the earlier reflective photodiodes.

The size of incident light 305 can be deigned to accommodate any desiredparameter or specification. In some cases, the size of incident light305 (e.g., when it is received at reflective photodiode 310) is within arange spanning 50 μm and 3 mm.

It will also be appreciated that incident light 305 can be any type oflight. For instance, incident light 305 can be red laser light, greenlaser light, blue laser light, and even infrared laser light, or anycombination of the above. As such, the red, green, blue, and IR lightcan be structured to span the range between 50 μm and 3 mm.Additionally, the incident light 305 can be combined light that combinesmultiple colors. The combined light may also be in the range specifiedabove.

It will be appreciated that the disclosed reflective photodiodes may beprovided within a compact package or unit. Having a small, compactreflective photodiode is beneficial for high frequency monitoring of theincident light. For instance, smaller reflective photodiodes allow forsmaller capacitance in the unit. Smaller capacitance allows for fastermonitoring of the incident light.

FIG. 3A also shows how the reflective photodiode 310 includes a highlyreflective (HR) coating 315 and a light receiving surface 320, which arerepresentative of the HR coatings and light receiving surfaces discussedearlier. When incident light 305 strikes the HR coating 315, a portionof the incident light 305 will pass or leak through the HR coating andwill be absorbed, measured, or otherwise received at the light receivingsurface 320 in the form of absorbed light 325.

Another portion of the incident light 305 will be reflected away fromboth the HR coating 315 and the light receiving surface 320 in the formof reflected light 330. It will be appreciated that the HR coating 315can reflect light spanning a large bandwidth. That is, HR coating 315 ishighly versatile and is able to beneficially reflect numerous differenttypes of light waves spanning many different wavelengths or bandwidthswhile simultaneously allowing a sufficient amount of leaked light topass through it for laser monitoring and control.

Turning briefly to FIG. 3B, this figure illustrates a samplereflectivity measurement 335 of the reflective coating (e.g., HR coating315 from FIG. 3A) on a reflective photodiode. FIG. 3B shows the samplereflectivity for blue color laser light 340, green color laser light345, and red color laser light 350 as used within a reflectivephotodiode in accordance with the disclosed embodiments. FIG. 3B alsoshows how the reflective surface of the reflective photodiode allows ahigh percentage (e.g., FIG. 3B indicates that in some cases, thepercentage can be around 98%) of the light to be reflected away.Consequently, a much lower percentage (e.g., around 2%) of the light isabsorbed by the reflective photodiode.

Returning to FIG. 3A, in cases where the incident light 305 is red laserlight, green laser light, blue laser light, infrared laser light, or anycombination of the above, reflective photodiode 310 is able to reflectand/or absorb portions of the red, green, blue, and infrared laser light(either before being collimated or after being collimated and eitherbefore being beam combined or after being beam combined). The reflectedportions of the red, green, blue, or infrared laser light can be withinthe ranges discussed earlier (e.g., 80%, 90%, 95%, 96%, 97%, 98%, 99% ormore than 99%) and the absorbed portions of the red, green, blue, orinfrared laser light can be within the other ranges discussed earlier(e.g., less than 20%, 10%, 5%, 4%, 3%, or even less than 2% such as 1%or even less than 1%).

Multi-Section Reflective Photodiode

In some cases, the reflective photodiode may be configured to receive asingle ray/beam of light, where the single ray of light includes asingle color or multiple colors (e.g., RGB and IR laser light). In othercases, the reflective photodiode may be configured to simultaneously orconcurrently receive multiple discrete rays of light, where each one ofthe different rays of light can be a single color or a combination ofmultiple colors. FIG. 4 shows an example scenario in which a reflectivephotodiode is specially configured to simultaneously receive and reflectmultiple different rays of light.

Specifically, FIG. 4 shows a multi-section photodiode 400 that includesa first section photodiode 405, a second section photodiode 410, and athird section photodiode 415. In some implementations, multi-sectionphotodiode 400 includes a red section photodiode (e.g., first sectionphotodiode 405) for absorbing and measuring a first portion of red laserlight, a green section photodiode (e.g., second section photodiode 410)for absorbing and measuring a first portion of green laser light, and ablue section photodiode (e.g., third section photodiode 415) forabsorbing and measuring a first portion of blue laser light.

While FIG. 4 shows that multi-section photodiode 400 includes threeseparate sections, it will be appreciated that multi-section photodiode400 may be equipped or designed to include any number of differentsections. As an example, multi-section photodiode 400 may include 2sections, 3 sections, 4 sections, 5 sections, and more than 5 sections.Furthermore, each section may be configured to absorb and measure asingle-color ray of light or, alternatively, each section may beconfigured to absorb and measure rays of light having multiple colors.In some implementations, one section may absorb one color of light whileanother section may simultaneously absorb multiple colors of light. Fromthis, it will be appreciated that the different sections can befabricated in numerous ways and can be designed to accommodate manydifferent applications.

FIG. 4 also shows how multi-section photodiode 400 includes a HR coating420, which is representative of the HR coatings discussed earlier. Inthis case, there is a single HR coating 420 uniformly covering all ofthe sections, but that may not always be the case. For instance, in someimplementations, each section may have its own separate HR coating suchthat the different HR coatings are separated or isolated from oneanother. In some implementations, an HR coating may uniformly cover 1,2, 3, 4, etc. photodiode sections while a separate HR coating mayuniformly cover 1, 2, 3, 4, etc. photodiode sections on the samemulti-section photodiode.

FIG. 4 also shows that in some cases, an isolation layer 425 may beprovided between each one of the sections. For instance, isolation layer425 is positioned between first section photodiode 405 and secondsection photodiode 410. Isolation layer 425 may be provided to ensureelectrical isolation or insulation between the different photodiodesections. In some cases, isolation layer 425 may be an etched portion ofthe multi-section photodiode 400, where the etching provides electricalisolation. In other cases, isolation layer 425 may be a dielectric layeror other type of isolation material that provides electrical isolation.In other cases, the isolation layer 425 can be a metal layer that blockslight between the photodiode sections.

It will also be appreciated that the dimensions of multi-sectionphotodiode 400 can be configured to suite any desired specification. Asan example, the separation distance 430 between the different photodiodesections can be set to any desired value. A typical value for separationdistance 430 is around 0.05 mm, though this value can vary as needed ordesired. In some cases, separation distance 430 can vary within a rangeof 0.01 mm up to 0.1 mm. Furthermore, the separation distance betweendifferent photodiode sections can be different, even on the samemulti-section photodiode 400. As an example, separation distance 430 isthe distance between second section photodiode 410 and third sectionphotodiode 415. In one example, separation distance 430 can be 0.05 mm.In contrast, the separation distance between first section photodiode405 and second section photodiode 410 can be a different value (e.g.,perhaps 0.04 mm or 0.06 mm). Accordingly, the separation distances canvary, even across different photodiode sections on the samemulti-section photodiode.

The dimensions of each respective photodiode section can also be set ordesigned to any value. For instance, width 435 and length 440 of eachphotodiode section can be set to any designed value. An example valuefor width 435 is around 0.3 mm and an example value for length 440 isaround 2.00 mm. Of course, other values may be used as well. Forinstance, width 435 may span any value in the range of 0.1 mm to 1.0 mm,and length 440 may span any value in the range of 1.00 mm and 4.00 mm.Similar to the earlier discussion, different photodiode sections mayhave different dimensions, even though they are placed on the samemulti-section photodiode (e.g., one section may be 0.3 mm by 2.00 mmwhile another section on the same multi-section photodiode may be 0.1 mmby 1.00 mm).

Pitch 445 represents the distance between congruent points onneighboring photodiode sections. For instance, pitch 445 is shown asbeing the distance between one point on second section photodiode 410and a corresponding point on third section photodiode 415. Pitch 445 maybe any value, but one example value is around 0.35 mm. In some cases,pitch 445 may be any value spanning the range between 0.1 mm and 4.0 mm.

FIG. 4 shows how incident light 450A is striking first sectionphotodiode 405, incident light 450B is striking second sectionphotodiode 410, and incident light 450C is striking third sectionphotodiode 415. The HR coating 420 allows some light to be absorbed bythe underlying respective photodiode sections while the remaining lightis reflected. For instance, reflected light 455A is the light reflectedoff of first section photodiode 405, reflected light 455B is the lightreflected off of second section photodiode 410, and reflected light 455Cis the light reflected off of third section photodiode 415.

It will be appreciated that multi-section photodiode 400 may berepresentative of any of the reflective photodiodes/turning opticsdiscussed previously. Specifically, multi-section photodiode 400 may bepositioned at any of the locations described earlier, such as, but notlimited to, being positioned before or after collimating optics andbefore or after beam combiners. Accordingly, the disclosed embodimentsare able to provide a highly flexible arrangement or placementconfiguration with regard to the multi-section photodiode.

Feedback Control of the Laser Assembly/Emitter

Attention will now be directed to FIG. 5A which refers to a number ofmethod acts that may be performed. Although the method acts may bediscussed in a certain order or illustrated in a flow chart as occurringin a particular order, no particular ordering is required unlessspecifically stated or required because an act is dependent on anotheract being completed prior to the act being performed.

FIG. 5A shows a flowchart of an example method 500 for dynamically (inreal-time) controlling the output of a laser emitter through the use offeedback provided by a reflective photodiode. That is, because laserperformance changes over temperature and time, it is highly beneficialto continuously or periodically measure/determine the laser'sperformance by monitoring its power output and operationalcharacteristics/parameters/attributes via the use of the photodiode. Indoing so, the embodiments are able to accurately determine the laser'slasing current threshold (i.e. the point at which the laser will beginto lase) as well as its slope efficiency (i.e. the relationship betweenthe laser's pump/drive current and its power output). Initially, method500 includes an act 505 of receiving incident light at a reflectivephotodiode (e.g., those discussed throughout this disclosure) thatincludes a light receiving surface and a reflecting coating, asdescribed earlier. The reflective photodiode can be a single sectionreflective photodiode or a multi-section reflective photodiode.Additionally, the received light can be generated by a single laser ormultiple lasers. Furthermore, the received light can be a single coloror it can be multiple colors.

Method 500 then includes an act 510 of causing the light receivingsurface to absorb a first portion of the incident light. For instance,the p-n junction of the photodiode can absorb the light as describedearlier in order to generate a photocurrent.

Act 515 includes a process of causing the reflective coating to reflecta second portion of the incident light while permitting the firstportion to pass through the reflective coating to be absorbed by thelight receiving surface.

Then, method 500 includes an act 520 of providing feedback to a laserassembly that emitted the incident light. For instance, the reflectivephotodiode is able to absorb light and convert the light into anelectrical current. By absorbing the light, the photodiode is able todetermine a current/instant power output and operational characteristicsof the laser assembly. Determining the power output is particularlybeneficial because it allows for reconfiguring, calibrating, orreadjusting of the laser's power output or other operations, as need.

Furthermore, it will be appreciated that the optical characteristics(e.g., the optical flatness and surface roughness) of the reflectivesurface are designed in a manner so that the reflective surface is ableto reflect a broad spectrum of wavelengths. To clarify, previously itwas mentioned how the reflective photodiode is able to intercept andreflect incident light while allowing some of that incident light to beabsorbed by a photodiode positioned underneath a layer of reflectivecoating. It is desirable for the reflective coating layer or portion ofthe reflective photodiode to have minimal impact on the attributes ofthe light it reflects. To clarify, it is desirable for the reflectivecoating to not bend the laser light in a manner that reduces thecoherence or spectral properties of the light. Instead, it is desirableto structure the reflective coating so that it just reflects the light.In accordance with the disclosed principles, the embodiments can bestructured in a manner where the optical flatness and surface roughnessof the reflective coating will have minimal or nominal impact on thelight qualities of the laser light. As such, the reflective photodiodehas sufficient optical quality to act as a turning optic. For instance,turning briefly to FIG. 5B, this figure illustrates a surface scan 525of a reflective photodiode showing the measured height profile of aphotodiode. As shown, the profile is substantially uniform across theentire X-Y plane. FIG. 5B also shows the surface profile 530 of thephotodiode. Again, the profile is substantially flat, with a surface bowof under 100 nm over the entire surface (e.g., here, the surface isapproximately 3 mm in width). Such a small amount or degree of surfacebow provides for a high degree of optical flatness and a low degree ofsurface roughness.

Determining the power output allows the system to recalibrate itself iftoo much or too little power is being expended (e.g., as a result ofchanges to lasing current threshold or slope efficiency resulting fromtemperature or environmental changes). As such, the reflectivephotodiode is able to provide feedback to the laser assembly. Thisfeedback is based on a measurement of the first portion of the incidentlight and is provided to control the output of the laser assembly.

FIG. 6 shows an example implementation of method 500 from FIG. 5A.Specifically, FIG. 6 shows an illumination system 600 that includes alight source 605 that is emitting incident light 610. Incident light 610is shown as striking a reflective photodiode/turning optic 615, which isrepresentative of the earlier reflective photodiodes and which may be asingle section photodiode or a multi-section photodiode. Some light willbe reflected by the reflective photodiode/turning optic 615's HRcoating, as shown by reflected light 620, while some light will beabsorbed, as shown by absorbed light 625.

The absorbed light 625 will be converted to an electrical current andwill be used to determine a current power output of the light source605. The value or measurement of the electrical current can then beincluded as feedback 630 to the light source 605 to determine whetherthe power output of light source 605 needs to be adjusted or calibratedin any manner.

Mixed-Reality Systems

Mixed-reality systems, including virtual-reality (VR) andaugmented-reality (AR) systems, have received significant attentionbecause of their ability to create truly unique experiences for theirusers. For reference, conventional VR systems create a completelyimmersive experience by restricting their users' views to only virtualenvironments. This is often achieved through the use of a head-mounteddevice (HMD) that completely blocks any view of the real world. As aresult, a user is entirely immersed within the virtual environment. Incontrast, conventional AR systems create an augmented-reality experienceby visually presenting virtual images (i.e. “holograms”) that are placedin or that interact with the real world.

As used herein, VR and AR systems are described and referencedinterchangeably. Unless stated otherwise, the descriptions herein applyequally to all types of mixed-reality systems, which (as detailed above)include AR systems, VR systems, and/or any other similar system capableof displaying virtual images. As used herein, the term “virtual image”collectively refers to images rendered within a VR environment as wellas images/holograms rendered in an AR environment.

Some, but not necessarily all, of the disclosed embodiments are operablein conjunction with a mixed-reality computing system (e.g., thelaser-based systems are able to generate the virtual images for themixed-reality computing system). In some cases, the mixed-reality systemincludes a microelectromechanical scanning (“MEMS”) mirror system. Asshown in FIG. 7A, a MEMS mirror system 700A is able to receive lightthat has been measured and reflected by a reflective photodiode inaccordance with the principles discussed earlier. Because FIG. 7A issubstantially similar to FIG. 2A, the common components have not beenrelabeled for brevity purposes.

As mixed-reality systems become smaller and smaller, it is highlydesirable to reduce the size of the laser and its associated components(e.g., the collimating optics, beam combiners, and photodiodes). Byproviding a multi-purposed photodiode, which operates as both aphotodiode and a high performance turning optic, the disclosedembodiments are able to beneficially reduce the size (and even thenumber) of hardware components used in the mixed-reality system. Assuch, the disclosed reflective photodiodes are particularly useful andbeneficial in mixed-reality systems. It will be appreciated, however,that the disclosed reflective photodiodes can be used in otherapplications, and they should not be limited solely to mixed-realitysystems.

FIG. 7B shows some components that may be included within a display fora mixed-reality computing system. These components are beneficiallyprovided to render the virtual images that were discussed earlier.Specifically, FIG. 7B shows a MEMS/laser unit 700B, which isrepresentative of MEMS mirror system 700A from FIG. 7A and whichincludes a laser emitter 705 that functions as a projector for themixed-reality display and that may be representative of the lightsources and lasers discussed earlier. Although not illustrated in FIG.7B, it will be appreciated that the MEMS/laser unit 700B mayadditionally include the reflective photodiodes that were discussedearlier.

Laser emitter 705 (or laser assembly) includes a (first) laser 705A, a(second) laser 705B, and a (third) laser 705C. Examples of these lasersmay be a red laser, a green laser, and a blue laser such that the laseremitter 705 is a red, green, blue (RGB) laser assembly having RGBlasers. While only three lasers are presently shown, it will beappreciated that laser emitter 705 may include any number of lasers.Moreover, in some embodiments, lasers 705A, 705B, and 705C may beincluded within their own different discrete laser assemblies. In someembodiments, an infrared (IR) laser may be included as a part of laseremitter 705 or within a separate assembly/emitter.

In some embodiments, such as the one shown in FIG. 7B, the laser lightfrom the lasers 705A, 705B, and 705C is optically/spectrally combined toform RGB laser light 710. That is, the laser light 710A from laser 705A,the laser light 710B from laser 705B, and the laser light 710C fromlaser 705C is optically/spectrally combined (e.g., either within thelaser emitter 705 or outside of the laser emitter 705) to produce asingle collimated beam of red, green, and blue RGB laser light 710(e.g., via use of beam combiner(s), collimating optic(s), and reflectivephotodiode(s), as described earlier). It will be appreciated that laserlight 710 may be a continuous beam of laser light, or, alternatively, itmay be a pulsed beam of laser light. In the example shown in FIG. 7B,the laser light 710 is a pulsed beam, as demonstrated by its dashed-lineillustration. It will also be appreciated that the laser light may passthrough any number of reflective photodiodes, either before or afterbeing spectrally combined and/or collimated, as discussed earlier.

The laser light 710 is then directed to a microelectromechanicalscanning (“MEMS”) mirror system 715. The MEMS mirror system 715 includesa multi-directional mirror array that is able to rapidly redirect andaim laser light to any desired pixel location. For example, scanningdirection 720 shows how the MEMS mirror system 715 is able to rapidlyredirect pulsed (or continuous) scanning laser light 725A and pulsedscanning laser light 725B to any location. Here, pulsed scanning laserlight 725A and 725B originate from the laser light 710. While only twoinstances of the pulsed scanning laser light (e.g., 725A and 725B) arelabeled, it will be appreciated that the MEMS mirror system 715 is ableto redirect any number of pulsed emissions. By scanning laser light backand forth horizontally and up and down vertically, the MEMS/laser unit700B is able to illuminate individual pixels of a virtual image within adesired field of view. Because the MEMS/laser unit 700B is able toilluminate individual pixels so rapidly, the MEMS/laser unit 700B isable to render an entire virtual image (e.g., an image frame) for a userto view and interact with without the user realizing that the virtualimage was progressively generated by scanning individual pixels.

In some embodiments, the MEMS/laser unit 700B includes more than onelaser emitter. For instance, FIG. 7B shows a (second) laser emitter 730.In cases where there are more than one laser emitter, then the emitterscan be configured to jointly or concurrently illuminate pixels togenerate an image frame. For instance, in some embodiments, an imageframe is illuminated by two separate laser emitters (e.g., laser emitter705 and laser emitter 730). In some cases, the two separate laseremitters concurrently illuminate corresponding pixels. In other cases,the two separate laser emitters stagger when pixels are illuminated.

FIGS. 8A and 8B provide further clarification by showing how aMEMS/laser unit 800A can be used in a VR environment and how aMEMS/laser unit 800B can be used in an AR environment, respectively.MEMS/laser units 800A and 800B are both example implementations of theMEMS/laser unit 700B from FIG. 7B. Pulsed laser light 805A in FIG. 8Aand pulsed laser light 805B in FIG. 8B are example implementations oflaser light 710 and pulsed scanning laser light 725A and 725B from FIG.7B.

In FIG. 8A, the display 810 is representative of a VR display. In a VRenvironment, the user's view of the real-world is entirely occluded suchthat the user is able to see only the VR environment. Here, display 810is shown as including a vertical field of view (“FOV”) and a horizontalFOV. FIG. 8A also shows the progressively backward and forwardhorizontal and upward and downward vertical scanning direction 815 inwhich the MEMS/laser unit 800A is able to scan individual images of avirtual image onto the display 810. By rapidly scanning/rastering theindividual pixels, the MEMS/laser unit 800A is able to render an entirevirtual image or even an entire VR environment.

It will be appreciated that each pixel rastered on the display 810 isgenerated by pulsing the laser included within the MEMS/laser unit 800A.In this manner, it is possible to illuminate each pixel on display 810in a pixel-by-pixel basis all the way from the top portion of thedisplay 810 to the bottom portion of the display 810. Consequently, asthe MEMS mirror system in the MEMS/laser unit 800A is scanned/aimed at agiven pixel position on the display 810, the laser is pulsed to adetermined intensity or power output level so as to properly illuminatethat pixel within the overall virtual image.

FIG. 8B shows an example implementation within an AR system. Instead ofscanning pixels on a display (e.g., display 810), the AR system causesits MEMS/laser unit 800B to scan pixels onto the user's eye through theuse of a waveguide 820, which receives the laser light and then directsthe laser light towards the user's eye.

To illustrate, FIG. 8B shows the MEMS/laser unit 800B generating pulsedlaser light 805B which is directed towards the waveguide 820. Thiswaveguide 820 includes an entry grating 825, through which the pulsedlaser light 805B enters the waveguide 820, and an exit grating 830,through which the pulsed laser light 805B exits the waveguide 820. Thewaveguide 820 is structured to enable the pulsed laser light 805B topropagate through it so that the pulsed laser light 805B can beredirected to a desired location, such as the scanning area 835. In manyinstances, the scanning area 835 corresponds to a user's eye. In thisregard, there is a display module (e.g., the MEMS/laser unit 800B) thatshines light into a waveguide (e.g., waveguide 820). Light is thenrefracted/reflected along that waveguide and then coupled out of thewaveguide towards the user's eye. As such, instead of scanning lightonto the display 810 in the VR scenario, pulsed laser light can bescanned to a user's eye in the AR scenario. Similar to the earlierdiscussion, the intensity or brightness of a pixel is referred to hereinas the illumination energy for that pixel.

Accordingly, some embodiments are directed to an illumination systemthat renders images in a mixed-reality system. This illumination systemmay include a laser assembly (e.g., light source 205 from FIG. 2A) thatincludes a red laser, a green laser, a blue laser, and/or an infraredlaser, where each one of the red laser, the green laser, the blue laser,and the infrared laser is associated with a corresponding collimatingoptic (e.g., collimating optic 240A from FIG. 2A) and where the redlaser emits red laser light, the green laser emits green laser light,the blue laser emits blue laser light, and the infrared laser emitsinfrared laser light. In some embodiments, the illumination systemincludes one or more collimating optics that collimate the laser lightgenerated by the laser assembly (e.g., a first collimating optic for thered laser light, a second collimating optic for the green laser light, athird collimating optic for the blue laser light, and a fourthcollimating optic for the infrared laser light).

The illumination system may additionally include a single sectionreflective photodiode and/or a multi-section reflective photodiodeconfigured in the manner described earlier. The single or multi-sectionreflective photodiode is configured to determine a power output of thelaser assembly by absorbing/receiving and measuring portions of thelaser light generated by the laser assembly.

The illumination system may also include a beam combiner (e.g., beamcombiner 245 from FIG. 2A) that combines portions of the red laserlight, portions of the green laser light, portions of the blue laserlight, and/or portions of the infrared laser light generated by thelaser assembly to form combined laser light. The illumination system mayalso include a MEMS mirror system that redirects the combined laserlight (or potentially uncombined laser light) generated by the laserassembly to illuminate pixels in an image frame for the mixed-realitysystem.

In some implementations, the single or multi-section photodiode ispositioned upstream of the beam combiner such that the single ormulti-section photodiode is positioned between the laser assembly andthe beam combiner relative to a path traveled by the red laser light,the green laser light, the blue laser light, and/or the infrared laserlight from the laser assembly to the beam combiner. In someimplementations, the single or multi-section photodiode is positionedupstream of the collimating optics of the red laser, the green laser,the blue laser, and/or the infrared laser such that the single ormulti-section photodiode is positioned between the laser assembly andthe collimating optics. In other implementations, the single ormulti-section photodiode is positioned downstream of the collimatingoptics and/or downstream of the beam combiner. In some implementations,the single or multi-section photodiode is positioned downstream relativeto the collimating optics and is positioned upstream relative to thebeam combiner.

Accordingly, the disclosed embodiments relate to an improved type ofreflective photodiode. Because the reflective photodiode has multiplefunctions/purposes, it can now be placed within the illumination systemat many different locations, thereby providing an increasingly flexiblearchitecture/design.

Example Computer System(s)

Attention will now be directed to FIG. 9 which illustrates an examplecomputer system 900 that may be used to facilitate the disclosed methodsand/or that may comprise one of the disclosed systems, architectures, orillumination systems. It will be appreciated that computer system 900may be configured within various form factors. For example, computersystem 900 may be embodied as a tablet 900A, a desktop 900B, or a headmounted device (HMD) 900C. The ellipsis 900D demonstrates that computersystem 900 may be embodied in various other forms too. For instance,computer system 900 may also be a distributed system that includes oneor more connected computing components/devices that are in communicationwith computer system 900, a laptop computer, a mobile phone, a server, adata center, and/or any other computer system. The ellipsis 900D alsoindicates that other system subcomponents may be included or attachedwith the computer system 900, including, for example, sensors that areconfigured to detect sensor data such as user attributes (e.g., heartrate sensors), as well as sensors like cameras and other sensors thatare configured to detect sensor data such as environmental conditionsand location/positioning (e.g., clocks, pressure sensors, temperaturesensors, gyroscopes, accelerometers and so forth), all of which sensordata may comprise different types of information used during applicationof the disclosed embodiments.

In its most basic configuration, computer system 900 includes variousdifferent components. For example, FIG. 9 shows that computer system 900includes at least one processor 905 (aka a “hardware processing unit”),input/output (“I/O”) 910, a MEMS mirror system 915, a laser assembly920A with laser driver circuitry 920B, and storage 925. As used inconjunction with computer system 900, laser assembly 920A should beinterpreted broadly to include the laser emitters, collimating optics,beam combiners, and reflective photodiodes that were discussed earlier.Accordingly, any of the previously mentioned lasing or optical devicesmay be included as a part of laser assembly 920A. Laser driver circuitry920B is configured to control the power output and emissions of thelasing and optical devices and/or control the operations of the laserassembly 920A (e.g., including any feedback or measurement performed byany reflective photodiodes).

Computer system 900 may also include a depth engine which includes anytype of 3D sensing hardware to scan and generate a spatial mapping of anenvironment. For instance, the depth engine may include any number oftime of flight cameras, stereoscopic cameras, and/or depth cameras.Using these cameras, the depth engine is able to capture images of anenvironment and generate a 3D representation of that environment.Accordingly, depth engine includes any hardware and/or softwarecomponents necessary to generate a spatial mapping (which may includedepth maps, 3D dot/point clouds, and/or 3D meshes) used to generate orinfluence virtual images.

Storage 925 is shown as including executable code/instructions 930.Storage 925 may be physical system memory, which may be volatile,non-volatile, or some combination of the two. The term “memory” may alsobe used herein to refer to non-volatile mass storage such as physicalstorage media. If computer system 900 is distributed, the processing,memory, and/or storage capability may be distributed as well. As usedherein, the term “executable module,” “executable component,” or even“component” can refer to software objects, routines, or methods that maybe executed on computer system 900. The different components, modules,engines, and services described herein may be implemented as objects orprocessors that execute on computer system 900 (e.g. as separatethreads).

The disclosed embodiments may comprise or utilize a special-purpose orgeneral-purpose computer including computer hardware, such as, forexample, one or more processors (such as processor 905) and systemmemory (such as storage 925), as discussed in greater detail below.Embodiments also include physical and other computer-readable media forcarrying or storing computer-executable instructions and/or datastructures. Such computer-readable media can be any available media thatcan be accessed by a general-purpose or special-purpose computer system.Computer-readable media that store computer-executable instructions inthe form of data are physical computer storage media. Computer-readablemedia that carry computer-executable instructions are transmissionmedia. Thus, by way of example and not limitation, the currentembodiments can comprise at least two distinctly different kinds ofcomputer-readable media: computer storage media and transmission media.

Computer storage media are hardware storage devices, such as RAM, ROM,EEPROM, CD-ROM, solid state drives (SSDs) that are based on RAM, Flashmemory, phase-change memory (PCM), or other types of memory, or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to store desired programcode means in the form of computer-executable instructions, data, ordata structures and that can be accessed by a general-purpose orspecial-purpose computer.

Computer system 900 may also be connected (via a wired or wirelessconnection) to external sensors (e.g., one or more remote cameras,accelerometers, gyroscopes, acoustic sensors, magnetometers, etc.).Further, computer system 900 may also be connected through one or morewired or wireless networks 935 to remote systems(s) that are configuredto perform any of the processing described with regard to computersystem 900.

During use, a user of computer system 900 is able to perceiveinformation (e.g., a mixed-reality environment) through a display screenthat is included with the I/O 910 of computer system 900 and that isvisible to the user. The I/O interface(s) and sensors with the I/O 910also include gesture detection devices, eye trackers, and/or othermovement detecting components (e.g., cameras, gyroscopes,accelerometers, magnetometers, acoustic sensors, global positioningsystems (“GPS”), etc.) that are able to detect positioning and movementof one or more real-world objects, such as a user's hand, a stylus,and/or any other object(s) that the user may interact with while beingimmersed in the scene.

A graphics rendering engine may also be configured, with processor 905,to render one or more virtual objects within a mixed-realityscene/environment. As a result, the virtual objects accurately move inresponse to a movement of the user and/or in response to user input asthe user interacts within the virtual scene.

A “network,” like the network 935 shown in FIG. 9, is defined as one ormore data links and/or data switches that enable the transport ofelectronic data between computer systems, modules, and/or otherelectronic devices. When information is transferred, or provided, over anetwork (either hardwired, wireless, or a combination of hardwired andwireless) to a computer, the computer properly views the connection as atransmission medium. Computer system 900 will include one or morecommunication channels that are used to communicate with the network935. Transmissions media include a network that can be used to carrydata or desired program code means in the form of computer-executableinstructions or in the form of data structures. Further, thesecomputer-executable instructions can be accessed by a general-purpose orspecial-purpose computer. Combinations of the above should also beincluded within the scope of computer-readable media.

Upon reaching various computer system components, program code means inthe form of computer-executable instructions or data structures can betransferred automatically from transmission media to computer storagemedia (or vice versa). For example, computer-executable instructions ordata structures received over a network or data link can be buffered inRAM within a network interface module (e.g., a network interface card or“NIC”) and then eventually transferred to computer system RANI and/or toless volatile computer storage media at a computer system. Thus, itshould be understood that computer storage media can be included incomputer system components that also (or even primarily) utilizetransmission media.

Computer-executable (or computer-interpretable) instructions comprise,for example, instructions that cause a general-purpose computer,special-purpose computer, or special-purpose processing device toperform a certain function or group of functions. Thecomputer-executable instructions may be, for example, binaries,intermediate format instructions such as assembly language, or evensource code. Although the subject matter has been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the described features or acts described above.Rather, the described features and acts are disclosed as example formsof implementing the claims.

Those skilled in the art will appreciate that the embodiments may bepracticed in network computing environments with many types of computersystem configurations, including personal computers, desktop computers,laptop computers, message processors, hand-held devices, multi-processorsystems, microprocessor-based or programmable consumer electronics,network PCs, minicomputers, mainframe computers, mobile telephones,PDAs, pagers, routers, switches, and the like. The embodiments may alsobe practiced in distributed system environments where local and remotecomputer systems that are linked (either by hardwired data links,wireless data links, or by a combination of hardwired and wireless datalinks) through a network each perform tasks (e.g. cloud computing, cloudservices and the like). In a distributed system environment, programmodules may be located in both local and remote memory storage devices.

Additionally, or alternatively, the functionality described herein canbe performed, at least in part, by one or more hardware logic components(e.g., the processor 905). For example, and without limitation,illustrative types of hardware logic components that can be used includeField-Programmable Gate Arrays (FPGAs), Program-Specific orApplication-Specific Integrated Circuits (ASICs), Program-SpecificStandard Products (ASSPs), System-On-A-Chip Systems (SOCs), ComplexProgrammable Logic Devices (CPLDs), Central Processing Units (CPUs), andother types of programmable hardware.

It will be appreciated that computer system 900 may include one or moreprocessors (e.g., processor(s) 905) and one or more computer-readablehardware storage devices (e.g., storage 925), where the storage devicesinclude computer-executable instructions that are executable by the oneor more processors to perform any method (e.g., method 500 presented inFIG. 5A). In this regard, computer system 900 is also highly flexibleand can perform numerous operations.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A reflective photodiode comprising: a lightreceiving surface configured to absorb a first portion of incoming lightdirected at the reflective photodiode and to convert the first portionof incoming light into electrical current; and a reflective coatingdisposed on the light receiving surface, wherein the reflective coatingis configured to reflect a second portion of the incoming light awayfrom the light receiving surface while permitting the first portion ofthe incoming light to pass through the reflective coating and to beabsorbed by the light receiving surface.
 2. The reflective photodiode ofclaim 1, wherein the reflective coating is configured to reflect atleast 90% of the incoming light.
 3. The reflective photodiode of claim2, wherein the reflective coating is configured to reflect at least 95%of the incoming light.
 4. The reflective photodiode of claim 3, whereinthe reflective coating is configured to reflect at least 98% of theincoming light.
 5. The reflective photodiode of claim 1, wherein thereflective photodiode is a turning optic that reflects the secondportion of the incoming light.
 6. The reflective photodiode of claim 5,wherein the turning optic is positioned upstream of a beam combiner suchthat the turning optic is positioned between a laser assembly and thebeam combiner relative to a path of light emitted from the laserassembly towards the beam combiner.
 7. The reflective photodiode ofclaim 5, wherein the turning optic is positioned upstream of acollimating optic such that the reflective photodiode is positionedbetween a laser assembly and the collimating optic relative to a path oflight emitted from the laser assembly towards the collimating optic. 8.The reflective photodiode of claim 1, wherein the first portion of theincoming light that is absorbed by the light receiving surface is lessthan 10% of the incoming light.
 9. The reflective photodiode of claim 8,wherein the first portion of the incoming light that is absorbed by thelight receiving surface is less than 5% of the incoming light.
 10. Thereflective photodiode of claim 9, wherein the first portion of theincoming light that is absorbed by the light receiving surface is about3% of the incoming light.
 11. An illumination system that renders imagesin a mixed-reality system, the illumination system comprising: a laserassembly that includes at least one of red, green, blue (RGB) lasers oran infrared (IR) laser; a microelectromechanical scanning (MEMS) mirrorsystem that redirects laser light generated by the laser assembly toilluminate pixels in an image frame for the mixed-reality system; and areflective photodiode comprising: a light receiving surface configuredto absorb a first portion of incoming light directed at the reflectivephotodiode by the laser assembly and to convert the first portion ofincoming light into electrical current; and a reflective coatingdisposed on the light receiving surface, wherein the reflective coatingis configured to reflect a second portion of the incoming light awayfrom the light receiving surface towards the MEMS mirror system whilepermitting the first portion of the incoming light to pass through thereflective coating and to be absorbed by the light receiving surface.12. The illumination system of claim 11, wherein a size of the incominglight when received at the reflective photodiode is within a rangespanning 50 μm and 3 mm.
 13. The illumination system of claim 11,wherein the reflective photodiode is a turning optic that reflects thesecond portion of the incoming light.
 14. The illumination system ofclaim 13, wherein the turning optic is positioned upstream of a beamcombiner included as a part of the illumination system such that thereflective photodiode is positioned between the laser assembly and thebeam combiner relative to a path of light emitted from the laserassembly towards the beam combiner.
 15. The illumination system of claim13, wherein the turning optic is positioned upstream of a collimatingoptic included as a part of the illumination system such that thereflective photodiode is positioned between the laser assembly and thecollimating optic relative to a path of light emitted from the laserassembly towards the collimating optic.
 16. The illumination system ofclaim 11, wherein the second portion of the incoming light constitutes amajority of the incoming light such that the majority of the incominglight is reflected by the reflective coating.
 17. An illumination systemthat renders images in a mixed-reality system by individually scanningindividual pixels of said rendered images, the illumination systemcomprising: a laser assembly that includes red, green, blue (RGB)lasers; a microelectromechanical scanning (MEMS) mirror system thatredirects laser light generated by the laser assembly to illuminatepixels in an image frame for the mixed-reality system; a beam combinerthat combines the laser light generated by the laser assembly; one ormore collimating optics that collimate the laser light generated by thelaser assembly; and a reflective photodiode comprising: a lightreceiving surface configured to absorb a first portion of the laserlight directed at the reflective photodiode from the laser assembly andto convert the first portion of laser light into electrical current; anda reflective coating disposed on the light receiving surface, whereinthe reflective coating is configured to reflect a second portion of thelaser light away from the light receiving while permitting the firstportion of laser light to pass through the reflective coating and to beabsorbed by the light receiving surface.
 18. The illumination system ofclaim 17, wherein the laser assembly further includes an infrared (IR)laser.
 19. The illumination system of claim 17, wherein the reflectivephotodiode determines a power output of the laser assembly and providesthe determined power output as feedback to control the laser assembly.20. The illumination system of claim 17, wherein the reflectivephotodiode is positioned within the illumination system at apre-collimated location or, alternatively, the reflective photodiode ispositioned within the illumination system at a post-collimated locationsuch that the laser light is collimated prior to being received at thereflective photodiode.